Embodiments of the present invention relate to the treatment of fluids in electrochemical cells to control levels of ions, particulates, and microorganisms in the fluid, and to regenerate the cells.
Fluid treatment apparatuses comprising electrochemical ion exchange cells can be used to treat fluids to, for example, selectively exchange ions present in fluids, remove contaminants from drinking water, reduce total dissolved solids (TDS), treat industrial or hazardous waste fluids and desalinate salt water, amongst other uses. Electrochemical ion exchange cells have water-splitting, ion exchange membranes between facing electrodes in a cell. When a current is applied to the electrodes by a cell power supply, water is irreversibly dissociated into H+ and OH− ions at the boundary between the cation and anion exchange layers of the membranes, causing cations and anions to be exchanged from the fluid stream passing through the cell. Electrochemical cells can be regenerated without using hazardous chemicals simply by reversing the applied electric potential while flushing the cell with a fluid. Also, to obtain continuous operation, two or more electrochemical cells can be connected to allow treatment of fluid in a cell while another cell is being regenerated. When the reverse electric potential is applied, the membranes are regenerated without the use of chemicals. The cell can also have a valve to control the flow of fluids during treatment and regeneration processes.
Electrochemical systems can be used to selectively control the level of ions in the treated fluid but typically do not remove sediment and particulates from the fluid stream. The solids typically found in fluids such as well water or even treated city water, include particulates and sediment, such as sand or dirt. City water can also contain lead or other heavy metal ions which should be removed. Industrial waste systems can also use reduction of particulate matter. In addition to the removal of ions from the fluid, it is desirable to also remove such particulates from the fluid stream. Fluids with high solids content can also clog up the membranes to limit their operational cycle and block orifices of the electrochemical cells.
Another problem is that hard water from wells or the city water supply can also contain dissolved compounds, such as for example calcium, magnesium or manganese compounds, and bicarbonate or sulfate salts. These salts can precipitate out in the cell and tubing during process cycles. For example, dissolved calcium carbonate compounds can precipitate out to accumulate on cell walls, tubing and membranes, requiring frequent replacement or cleaning of these components. Scale accumulation in the cartridges, cells or tubing increases fluid inlet pressure requirements and reduces flow rates through the cell. Dissolved calcium compounds that precipitate out during membrane regeneration also clog the membrane with scale or particulates to reduce cell performance.
In fluid treatment processes, it is also desirable to reduce the level of microorganisms, such as germs, microbes, and even viruses, which are present in the treated fluid stream. Failure to properly disinfect drinking water can have severe consequences. For example, cryptosporidium, a contaminant of drinking water, caused the sickness of over 400,000 people in Milwaukee, Wis. Such microbes can be present in the original fluid before treatment and/or be actually generated and added to the fluid stream during the fluid treatment process itself. Microorganisms present in the original fluid can be removed by conventional bacteriolysis, disinfection or sterilization of the fluid prior to fluid treatment by ion exchange. The microbial growth generated within the fluid treatment apparatus can also be reduced by periodic cleansing of the fluid treatment system. However, such cleanings are often ineffective because they only partially remove the organic bio-residues formed on the inner walls of the fluid treatment systems as many of the inner surfaces of the components of such systems are difficult to access. Also, scrubbing the inner surfaces of the apparatus to completely remove the strongly adhered film, can result in scratches to which later formed biofilms are even more strongly adhered, and consequently all the more difficult to remove.
Conventional membrane regeneration processes can also take too much time to perform and use excessive fluid or electrical power for regeneration. Reducing the time it takes to regenerate a membrane allows the cell to be used for a larger number of process cycles per unit time. Minimizing the power required to regenerate membranes both reduces energy costs and minimizes scale formation which is typically promoted by temperature gradients. In water filtration applications, excessive waste fluid volume during regeneration further adds to operational costs. In industrial applications, the fluid used to regenerate the membranes may be expensive, difficult to procure or hazardous—particularly in chemical filtration systems, and thus, difficult to dispose of under prevalent environmental regulations. Thus, it is desirable to optimize membrane regeneration processes to reduce regeneration time, and fluid and energy consumption.
Other problems arise in treating fluids for drinking water applications. During the regeneration cycle, water is passed through the cell to remove ions and flush out residual solids. However, a small portion of the regeneration water stream may become entrapped in the cell after the regeneration process is completed. When the user subsequently turns on the cell for the first time, the cell discharges the residual entrapped fluid which may have sediments, be colored or have an undesirable taste. The same problem arises when the orifice is shut off when the cell is not in use, which can cause the residual fluid in the cell to become ionized with ions permeating out of the cell and into the stagnant cell water; thus, losing the benefit of the treatment process. Also, variations in quality of the fluid passed through the cell can affect both treatment and regeneration cycles. The ion composition, hardness, pH, pressure and other water source characteristics in city water supplies often varies during the day or from one city to another. Higher ambient water temperatures can alter the treatment and regeneration properties of the heated or cooled water. Furthermore, when normal cell electrode power levels are applied to hot input fluid streams, the output fluid can have excessively high temperatures. Variability in the amount of hard calcium salts in the input water can also cause undesirable fluctuations in fluid treatment and regeneration.
It is desirable to have a fluid treatment apparatus comprising an electrochemical cell which can efficiently treat fluids to control the level of ions in the fluid, remove sediments and particulates, and treat fluids that vary in ion content or type, hardness, pH, temperature and pressure. It is further desirable to be able to regenerate membranes faster, more thoroughly, and with reduced fluid consumption and electrical power usage. It is further desirable to deactivate and prevent reproduction of, remove, or reduce the levels of microorganisms in the fluid.